Soil nitrogen dynamics and maize yields in a Gliricidia Sepium-maize intercrop in Southern Malawi
1999
Ikerra, S. (International Centre for Research in Agroforestry, Nairobi (Kenya)) | Smithson, P.C. | Maghembe, J.A. | Buresh, R.J. (Mlingano Soils Research Institute, Tanga (Tanzania))
Many soils of southern Africa are severely deficient in N, but inorganic fertilizers are frequently unaffordable for most farmers. Leguminous fallows or intercrops can alleviate N deficiency, but N use efficiency of organic inputs may be low due to non-synchrony of N release and crop N requirements. We monitored soil inorganic N dynamics for two seasons in a gliricidia [Gliricidia sepium (Jacq.) Walp.]- maize (Zea mays L.) intercrop in the unimodal rainfall area of southern Malawi. Treatments were plus or minus gliricidia, and N at 0, 24 or 48 kg N ha-1 in factorial combination. Application of gliricidia prunings significantly (p 0.001) increased topsoil (0-20 cm) inorganic N at the end of the dry season. Fertilization alone also increased topsoil N (p 0.001 ), but accumulated 38 to 41% less N than the tree plots. Differences between tree and fertilized plots became non-significant by 4 weeks after planting. Tree plots accumulated significantly (p 0.01) more ammonium-N during the dry season. Nitrate-N remained constant during the dry season but rose rapidly in tree plots after the onset of rains. Both tree biomass and inorganic N significantly (p 0.001) increased maize grain yields. Pre-season inorganic N accounted for 71% of the variation in maize yields for the two seasons data combined. A 2- factor model including pre-season inorganic N and anaerobic N mineralization potential accounted for 84% of the variability in maize yields for the two seasons data combined, Pre-season inorganic N could be used to adjust or eliminate basal applications of N in seasonal rainfall areas, particularly in seasons preceded by a drought year. Delayed timing of biomass additions may increase N use efficiency by the crop.
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